Then Again, Maybe I Won't by Judy Blume

Ever since his dad got rich from an invention and his family moved to a wealthy neighborhood on Long Island, Tony Miglione's life has been turned upside down. For starters, there's his new friend Joel, who shoplifts. Then there's Joel's sixteen-year-old sister, Lisa, who gets undressed every night without pulling down her shades. And there's Grandma, who won't come down from her bedroom. On top of all his other worries, Tony has questions about growing up... Why couldn't things have stayed the same?